Jude 1:20
But ye, beloved, building up yourselves on your most holy faith, praying in the Holy Ghost,
Your most holy faith is your peak level of faith at that time.
As you speak in tongues, you build up yourself from that peak level that you have already attained. You build yourself up like a giant.
The Amplified Classic Version says,
Jude 1:20 AMPC
But you, beloved, build yourselves up [founded] on your most holy faith [make progress, rise like an edifice higher and higher], praying in the Holy Spirit
